A tape recording device (a tape drive) is a sequential access device. Drive operations include mount/load and unmount/unload of a tape cartridge. Tape operations include operations on a tape medium which are position movement (a Position command), writing (a Write command), reading (a Read command) and synchronization (Sync command: Synchronize).
Data to be written in the tape includes user data and a file marker (FM) representing a user data delimiter. A write operation is performed either in a write-append method in which data is written in the tape from a position past the end of data after the tape is moved, or in an overwriting method in which old data is overwritten with new data.
Normally, the tape drive is able to perform read and write operations in a mixed manner, and these operations involve a moving operation and a synchronization operation (flush). The synchronization and moving operations cause the tape to move in a longitudinal direction thereof, thereby lowering the Read and Write performance of the tape drive. Note that the synchronization operation is an operation of ensuring that data temporarily stored in a buffer is written in a tape medium.
A hierarchical storage management (HSM) system allows the mixed read and write operations to be performed on tape drives. The tape drive is also included in a tape library which is at a lower layer of the HSM system. A single tape drive, however, is not required to perform read and write operations in a mixed manner in order to prevent the lowering of the overall performance of the entire read and write processing.
Instead, the single tape drive performs either the write operation or the read operation for each mount of a tape cartridge. Alternatively, a plurality of tape drives may each be used for either of write and read operations. These techniques require more tape drives, increase time-consuming (effort-taking) mount operations, and thus lower the processing performance.
There are some environments in which a tape cartridge is used exclusively for a read or write operation. Large-scaled scientific and technical calculations, in particular, cannot achieve higher performance, if a single tape cartridge is used for both mixed read and write operations. This also holds true for a hierarchical storage system which includes general tape storage devices.
Japanese Patent Application No. 2009-294309 provides a mechanism for causing a tape drive to perform read/write operations in a mixed manner in a single cartridge. Here, the writing method is an append writing method (Append Write). In the append writing method, the end of data (EOD) of write data in a tape is sequentially brought back by using a sequential moving method of the tape drive.
The writing method of a tape drive, however, includes Over Write in addition to the append write. The Over Write command is used to overwrite data (for example, a data set) having been written on a tape with new data by using the append write.
Accordingly, it is necessary to consider a case where the Over Write is received in mixed read/write operations in a single tape drive and tape cartridge.